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It has been pointed out in the literature that in the presence of an external magnetic field the axion mass receives an electromagnetic contribution. We show that if a magnetic field with energy density larger than ∼10 −8 times the energy density of the Universe existed at temperatures of a few GeV, that contribution would be dominant and consequently the cosmic evolution of the axion field would change substantially. In particular, the expected axion relic abundance would be lowered, allowing a small relaxation of the present cosmological bound on the Peccei-Quinn constant.

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The combined process of epitaxy and ion implantation has been developed in the fabrication of a buried-channel WN x /W self-aligned GaAs metal-semiconductor field-effect transistor (MESFET). This MESFET comprises an ion-implanted channel and an undoped GaAs epitaxial surface layer. The ion-implantation technique leads to an IC-oriented process and the epitaxial technique to a buried channel structure. Both ease of isolation and enhanced breakdown voltage were attained, promising monolithic microwave integrated circuits (MMICs) for L-band digital mobile communication systems.